The present invention relates to a private switched communications system having at least two PBX systems connected through CCITT primary rate interfaces to an ISDN (Integrated Services Digital Network) public network.
With current private switched networks, the number of dedicated or leased tie trunks between PBXs (private branch exchanges) is usually determined to meet peak traffic load. However, the amount of business traffic varies significantly during the day as well as from day to day, and hence the cost performance of the tie trunks is low.
It is thus desirable to establish tie trunks between PBXs on an as-needed basis to cost-effectively meet varying traffic volume.